For use in a type of internal combustion engine in which fuel is injected directly into a cylinder, there has been known a fuel injection control system equipped with a low pressure fuel pump for sucking fuel from a fuel tank and a high pressure fuel pump for boosting the pressure of the fuel sucked by the low pressure pump to a pressure that allows injection into the cylinder.
In the above-described fuel injection control system, it is desired in order to reduce energy consumption in the operation of the low pressure fuel pump that the discharge pressure (or feed pressure) of the low pressure fuel pump be made as low as possible. However, if the pressure in a section between the low pressure fuel pump and the high pressure fuel pump becomes lower than the saturation vapor pressure of the fuel, vapor might be generated in the high pressure fuel pump.
As a countermeasure against this, Patent Document 1 describes a technology in which when the duty cycle of the high pressure fuel pump becomes equal to or larger than a predetermined value, the feed pressure is raised on the assumption that vapor is generated.
Patent Document 2 describes a technology in which a vapor pressure sensor is provided in the fuel tank and the fuel type is identified by comparing the measurement value of the vapor pressure sensor and measurement results obtained by measurements conducted in advance.
Patent Document 3 describes a technology in which the pressure and temperature of LPG in the fuel tank are measured by a fuel temperature sensor and a fuel pressure sensor, and a vapor pressure curve of the LPG in use is determined by comparing the measurement results with previously stored vapor pressure curves.
Patent Document 4 describes a technology pertaining to a vaporized fuel processing apparatus for supplying vaporized fuel generated in the fuel tank to the intake system of the internal combustion engine. In this technology, the vaporized fuel concentration in the mixture is obtained and the volatility of the fuel is determined based on the vaporized fuel concentration thus obtained.
Patent Document 5 describes a technology in which a temperature sensor for measuring the temperature in the fuel tank, a pressure sensor for measuring the pressure in the fuel tank and a density sensor for measuring the density of fuel supplied to the internal combustion engine are prepared and the octane number of the fuel is determined based on the results of measurement by the sensors at the time of the first start-up after fuelling.
Patent Document 6 describes a technology in which a heater for heating the fuel taken into a fuel identification chamber from a fuel passage to a predetermined temperature and a temperature sensor for measuring the temperature of the heated fuel are prepared and properties of the fuel are identified based on the results of measurement by the temperature sensor and pressure sensor.
Patent Document 7 describes a technology in which when mis-fuelling is found based on the result of identification of fuel properties, emergency driving is enabled by increasing the idle engine speed of the internal combustion engine and prohibiting high load driving.
Patent Document 8 describes a technology in which when a low octane fuel is used, the fuel injection timing is retarded, the fuel injection pressure is raised, and the ignition timing is advanced, thereby avoiding pre-ignition and preventing the torque decrease.
Patent Document 9 describes a technology in which a calculation model for calculating the fractionated amount of a fuel based on the saturation vapor pressures of a plurality of components contained in the fuel and the mix proportion of the plurality of components is prepared, and a mixture proportion at which the value calculated according to the calculation model becomes equal to a fractionated amount measured in advance is determined.